Rotary die cutting machines are used to perform cutting and scoring operations in numerous industries including in the manufacture of corrugated products such as boxes and shipping containers. Generally, the rotary die cutting machines pass a continuously moving workpiece through the nip of a cutting die and a rotary anvil. The cutting die includes blades that project from the surface thereof to provide desired cutting and scoring actions to the workpiece. The rotary anvil supports the workpiece and includes thereon one or more resilient cutting mats which are aligned around the circumference of the anvil. The cutting mats are typically formed from a resilient polymeric material. The cutting mats serve as a backstop allowing the cutting die blades to be urged against the workpiece without damaging the blades themselves or the surface of the anvil. However, being subjected to repeated contact with the die cutting blades causes surface wear and tear on the mats and requires that the mats be frequently changed out or replaced.
Cutting mats are typically manufactured to include a backing or support layer beneath the resilient polymer to provide stiffness and aid in mounting the mats onto rotary anvil cylinders. Generally, the use of such backing materials has led to problems such as increased weight, lack of flexibility which complicates installation, and the inability of the backing material to hold and maintain a uniform, flat surface across the width of cutting mat. This inability to hold and maintain a uniform, flat surface is often referred to as “cupping.” Cupping may be defined as the width of a gap which forms between the backing material of the cutting mat and the surface of the rotary anvil cylinder when the mat is installed. These gaps cause the upper working surface of the mat to have high spots such that the surface is not planar. The use of a steel backing layer has this cupping problem.
With the development of new technologies available in corrugate manufacturing, the functionality of cutting mats is changing. In the past, cutting mats could be rotated or moved to different positions on an anvil cylinder to extend their useful lives. Cupping, while a nuisance, was largely ignored. Current rotary die cutting equipment, however, is equipped with the ability to grind or dress the working surface of a cutting mat. The ability to resurface the cutting mat during operation has increased the useful life of a mat, while rendering obsolete the need to rotate or move the mats. This improvement in equipment has made the need to reduce or eliminate cupping of the cutting mats a greater priority.
With the use of abrading or grinding cylinders in rotary die cutting equipment, those portions of the surfaces of the mats, which are raised across the width of the mats due to cupping is removed. However, the gap that exists between the anvil cylinder and cutting mat backing remains. During operation of the rotary die cutting equipment, pressures applied by both the rotary cutting dies and corrugate as it is being cut or scored pushes downwardly on the mat surface and reduces the gap. This “closing” or reduction of the gap in turn results in what has been referred to as low spots on the surfaces of the cutting mats. These low spots result in imperfections or voids in the finished corrugated product, because the cutting or scoring process is incomplete. These imperfections result in increased scrap corrugate, and may cause the end user to reject the cutting mats as defective.
Accordingly, there remains a need in the art to reduce or eliminate cupping of cutting mats used in rotary die cutting equipment.